The story of the tides is complicated by the fact that the influence of the Sun and Moon varies with the distances of the Moon and Sun from different parts of the Earth. When the positions of the Sun and Moon are at right angles to each other in relation to the Earth, as at half Moon, their tide rising effects act in opposition and neap tides occur (the lowest high tides and the highest low tides). But when the Sun and Moon are diametrically opposed to one another at full Moon, or when they are both on the same side of the Earth at New Moon, their tide generating effects are complementary and spring tides occur (the highest high tides and the lowest low tides). Spring tides have a range (the difference in level between successive high and low waters) thee times greater than that of neap tides.
Earth tide (Wikipedia)